1. Field of the Invention
The present invention relates to a microwave plasma etching method and apparatus for use in the manufacturing process of semiconductor devices and other similar electronics devices, wherein the apparatus may have applications such as the substrate surface etching process, the thin film formation or deposition on the substrate surface, and other types of the surface processing that involve the use of the plasma produced by the electron cyclotron resonance phenomenon.
2. Prior Art
The apparatus of the class as disclosed herein is currently available in two different types. One type is the apparatus that is described in Japan Published unexamined Patent Application No. Showa 56-155535. According to the microwave plasma processing technique as disclosed and taught in the publication cited above, a coil 3 is adapted to produce a magnetic field having a specific strength to be applied across a plasma formation chamber 1. A microwave generator 6 supplies a microwave energy into the plasma formation chamber 1 via a microwave energy waveguide 5 and a microwave inlet window 4, causing an electron cylotron resonance phenomenon to be produced within the plasma formation chamber 1. The energy that results from the electron cyclotron resonance interacts with a gaseous substance that has been introduced into the plasma formation chamber 1 through a gas supply source 7, thereby changing the gaseous substance into a plasma (as shown at 9). The plasma that has been created within the plasma formation chamber 1 is then fed as a plasma stream through its outlet window 14 into a substrate processing chamber 2, by utilizing the divergent magnetic field created by the above-mentioned magnetic field. In the substrate processing chamber 2, a subtrate 15 to be processed, such as etching, is placed on its holder 10, and undergoes the etching process by the impact of the ionized gases against the surface of the substrate 15. In FIG. 3, reference numeral 12 designates a gas discharge port.
The other type is the apparatus that is described in Japan Published unexamined Patent Application No. Showa 60-1334423. In the microwave plasma processing techinique as disclosed and taught in that publication and shown in FIG. 4a and FIG. 4b, a plasma formation chamber 1 is also used, and a gradient magnetic field is applied across the plasma formation chamber 1. A microwave energy passes through a waveguide 5 and a microwave inlet window 4, and is introduced intothe plasma formation chamber via a quartez bell jar 13. The plasma formation chamber 1, which is located within the bell jar 13, has not the arrangement such that it can meet the requirements for the microwave cavity resonator, and a substrate holder 10 is placed within the plasma formation chamber 1 which also serves as the substrate processing chamber. From the above publication, it can only be seen that the substrate holder 10 is located within a distance of 300 mm away from the point where the maximum magnetic density is produced along the center axis through the plasma formation chamber 1 and in the direction of travel of the microwave. No other information is presented. But it may be evident from other relevant publications such as the "Nikkei Micro Devices" (p. 61, Jun. 1988) and the "SEMI Technology Symposium" (pp. 133-144, 1988), both of which discuss the apparatus in detail, that the substrate holder 10 is placed at the point where less than 800 Gauss is produced and which is located 2 cm away from the point where 875 Gauss is produced as the electron cyclotron resonance point when the microwave frequency of 2.45 GHz is applied.
The prior art technologies as described above have the respective disadvantages which will be described specifically below. For the type of apparatus mentioned first, when the geometrical pattern configuration formed on the substrate 15 surface by the etching process, which includes a center area a, a peripheral area b of 100 .phi., and the area c of 150 .phi.in the neighborhood of the peripheral area b as shown in FIG. 5, is microscopially observed, it may clearly be seen that the center area a has the pattern configuration which is normal to the substrate surface, but the configuration tends to have a greater incline with reference to the substrate surface toward the outer peripheral area. This tendency becomes more evident when a substrate to be processed has a greater diameter. The reasons for this may be explained as follows:
The plasma produced within the plasma formation chamber is placed under the influence of the divergent magnetic field applied across the plasma formation chamber, and goes as a plasma stream toward the substrate surface. The geometrical pattern configuration that is formed on the substrate surface may largely depend upon the angle of incidence at which the ionized gases strike against the substrate surface. The ions that contribute to the etching process are incident at inclined angles with reference to the substrate surface, particularly when striking against the outer peripheral area thereof. Thus, the outer peripheral area may present pattern forms that are inclined inwardly toward the inside. It may also be observed that the ionized gases have a low current density that may result in an increased ion energy, which causes defects to be introduced under the substrate surface.
It may also be observed that when the ionized gases are drawn out by the divergent magnetic field, they must travel over a long distance until they reach the substrate surface. During the travel, the ions may be scattering, and the scattered ions may cause more side etching.
It may readily be understood from the preceding description that there are several problems associated with the firstly mentioned type of the apparatus. Specifically, those problems are that the uniform etching pattern cannot be provided over the entire substrate surface, that the ions have the great energy, and that the side etching may easily be introduced.
Similarly, the problem associated with the secondly mentioned type of the apparatus is that the ion current density may be increased to some extent as compared with the first type of the apparatus, but the location where a substrate to be etched is placed deviates from the electron cyclotron resonance point. This requires that the energy of the ions incident upon the substrate surface be greater as shown in FIG. 6, and the substrate cannot exhibit any anisotropic etching property, even if a high bias voltage is applied across the substrate.